There has been a push in recent years to move away from fossil fuels as an energy source. The move towards what are generally characterised as cleaner fuel sources has seen significant development in the use of solar or wind energy as a means of providing usable forms of energy.
By its very nature, solar energy's biggest pitfall is the fact that at certain times of the day, the sun is unable to provide the necessary flux of photons to various devices that utilise solar energy. Similarly, wind turbines and the like are only effective when there is sufficient wind strength to drive them.
Interrupted or inconsistent supply of energy from a source makes it, in many instances, unreliable and also uneconomical.
In addition, at certain times, the sun's rays can be so excessive that the resultant heat and energy are dissipated as over-supply, rather than being usable by a solar-powered device.
A previous attempt to address the above difficulties used a silicon metalloid material as a means of storing thermal energy inside the material for use at a later time, for example, when solar input was no longer available, such as during the evenings or times of inclement weather. During peak solar activity the silicon metalloid material would absorb thermal energy as it underwent a phase change from a solid to a liquid.
Silicon metalloid material is characterised in part by the property that on undergoing a phase change from liquid to solid, there is an expansion of the material rather than contraction as would be expected for most other materials.
The thermal energy stored within the silicon metalloid material could be converted into electrical and/or mechanical action through electrical devices such as a Stirling engine and so forth, thus providing a source of power at times when solar activity was not available.
A disadvantage of silicon metalloid material is that it requires significant, care and understanding of its physical transformation during its expansion and contraction as it absorbs and releases thermal energy during phase changes. The expansion and contraction of the silicon metalloid material creates significant build-up of pressure on an enclosure in which it is placed. For example, if silicon metalloid material in the form of ingots is placed directly in contact with a refractory heat-absorbing material such as graphite, the metalloid would be absorbed by the graphite on undergoing a phase change to its liquid form. If the silicon metalloid is stored in a separate enclosure before being inserted into the refractory material, the continual pressure build-up and collapse of the silicon metalloid ingots as they undergo phase changes can result in fissuring of the enclosure.
If the ingots are stored within separate enclosures there would also be a need for the enclosure of the silicon metalloid ingots to efficiently transport heat, released during phase change of the silicon metalloid material, to the surrounding graphite.
PCT Application PCT/AU2010/001035 (published as WO 2011/017767), the contents of which are hereby incorporated in their entirety by reference, sought to address these problems by providing an enclosure in the form of an elongate canister formed of ceramics, the elongate canister including a pressure dispersion punt and a series of grooves in one of its ends, the series of grooves acting as a heat sink. In the thermal energy storage apparatus described in PCT/AU2010/001035, a series of such canisters are used to store silicon metalloid, and are packed in interleaved arrangement with a series of sintered graphite rods. It has been found, though, that in such an arrangement the canisters are prone to cracking, particularly in the region of the grooves.
It would be desirable to overcome or alleviate the above mentioned difficulties, or at least provide a useful alternative.